We only take app orders and never our own. Is this still useful as restaurant delivery software?

Yes, and it costs nothing extra on top of your plan. All your app orders arrive on one orders board and one kitchen screen, with Accept and Refuse in one place, and the day's real total in your reports. Your own ordering page comes with the plan anyway, so the moment you print its link on a receipt you have a door the apps do not take a commission on. Restaurant delivery software that only shows one app at a time is what a kitchen with three tablets is living with now. The Orders from delivery apps tab in the docs explains the one board.